Chromones Featuring\na [6,6]-Spiroketal Moiety Produced\nby Coculture of the Endophytic Fungi <i>Chaetomium virescens</i> and <i>Xylaria Grammica</i>

Under\nthe guidance of HPLC-DAD analysis, ten new chromones\nfeaturing\na rare [6,6]-spiroketal moiety, namely chaetovirexylariones A–J\n(<b>1</b>–<b>10</b>), together with two known congeners\n(<b>11</b>–<b>12</b>), were isolated from coculture\nof the endophytic fungi <i>Chaetomium virescens</i> and <i>Xylaria grammica</i>, from the rhizome of the medicinal plant <i>Smilax glabra</i> Roxb. Their structures were elucidated via\na combination of NMR and HRESIMS data, and the absolute configurations\nof <b>1</b>–<b>10</b> were determined by the chemical\nconversion and single-crystal X-ray diffraction (Cu Kα) experiments,\nas well as the comparison of the experimental and calculated electronic\ncircular dichroism (ECD) data. Compound <b>6</b> is the first\nreport as a racemate of this type of natural product. Compound <b>10</b> represents the first example of a [6,6]-spiroketal chromone\nbearing a 5-amino-3-methyl-2-pentenoic acid fragment. Compound <b>8</b> demonstrated a reduction in PTX resistance of SW620/AD300\nby a factor of 45, and had the potential to be an effective P-gp inhibitor\nand an antitumor chemotherapy sensitizer.